Wireless communication systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., time, frequency, and power). Examples of such multiple-access systems include code-division multiple access (CDMA) systems, time-division multiple access (TDMA) systems, frequency-division multiple access (FDMA) systems, and orthogonal frequency-division multiple access (OFDMA) systems.
By way of example, a wireless multiple-access communication system may include a number of base stations, each simultaneously supporting communication for multiple user equipments (UEs). A base station may communicate with UEs on downlink channels (e.g., for transmissions from the base station to the UE) and uplink channels (e.g., for transmissions from the UEs to the base station).
Some modes of communication may enable communications with a UE over different radio frequency spectrum bands (e.g., a licensed radio frequency spectrum band or an unlicensed radio frequency spectrum band) of a cellular network. With increasing data traffic in cellular networks that use a licensed radio frequency spectrum band, offloading of at least some data traffic to an unlicensed radio frequency spectrum band may provide a cellular operator with opportunities for enhanced data transmission capacity. Prior to gaining access to, and communicating over, the unlicensed radio frequency spectrum band, a transmitting apparatus may, in some examples, perform a listen before talk (LBT) procedure to contend for access to the unlicensed radio frequency spectrum band. An LBT procedure may include performing a clear channel assessment (CCA) to determine whether a channel of the unlicensed radio frequency spectrum band is available. When it is determined that the channel of the unlicensed radio frequency spectrum band is not available (e.g., because another device is already using the channel of the unlicensed radio frequency spectrum band), a CCA may be performed for the channel again at a later time.
In some cases, transmissions by one or more nodes over an unlicensed radio frequency spectrum band (e.g., Wi-Fi nodes or nodes of other operators) may prevent a base station or UE from gaining access to the unlicensed radio frequency spectrum, resulting in the base station or UE being “starved” of use of the unlicensed radio frequency spectrum band. In some cases, this starvation problem may be mitigated by using an LBT protocol configured for load based equipment (LBT-LBE) instead of an LBT protocol configured for frame based equipment (LBT-FBE). In an LBT-LBE protocol, an extended CCA procedure including a plurality of N CCA procedures may be performed. The extended CCA procedure performed in conjunction with an LBT-LBE protocol may provide a base station or UE a better chance to gain access to an unlicensed radio frequency spectrum band (e.g., compared to a single CCA procedure performed in conjunction with an LBT-FBE protocol).